1. Field of the Disclosure
This disclosure describes a method and reactor suitable for reformation of fuels at low temperatures and at low reaction pressures while using fine catalyst powders.
2. Description of Related Art
Reforming reactions are endothermic in nature and cannot be easily practiced at the low exhaust gas temperatures (<400° C.) associated with internal combustion engine exhaust. A high efficiency reactor is needed to transfer the heat from the exhaust gases to the reforming reactor. U.S. Patent Application Number 2007/0028860 describes a method and apparatus for fuel reforming using the exhaust gases from internal combustion engines and high temperature combustion processes in which a fuel reforming and steam mixture is introduced into a tube bundle having a plurality of heat exchange tubes, and heat from the exhaust gases is transferred into the heat exchange tubes thereby increasing the temperature of the mixture. The heated mixture is reformed by contact with a reforming catalyst external to but proximate to the exit of the tube bundle forming a reformed fuel. Catalyst beds in the form of fluidized beds or recirculating beds are taught; these catalysts are not compact and do not lend themselves well to an internal combustion engine process train.
U.S. Pat. No. 6,508,209 (to Collier, Jan. 21, 2003) describes the utilization of waste heat from an internal combustion engine for reforming of fuels. Natural gas and/or propane is fed into a reforming reactor for the purpose of converting or reforming a portion thereof to a gas containing methane and/or propane, steam, nitrogen, carbon dioxide, hydrogen and carbon monoxide. This gas is mixed with air and fed to the internal combustion engine. A catalyst bed is contained between two concentric cylinders, and the fuel, water and air are introduced to the catalyst bed. The engine exhaust gas is introduced to the smaller cylinder and is used for pre-heating the fuel and water and the catalyst bed for the purpose of reforming the fuel. The catalyst is coated on raschig rings or on a monolith comprised of cordierite. The preferred catalyst is nickel. A reformer containing such catalysts may lend itself well to large scale stationary applications, but is handicapped by poor heat transfer and catalyst flake-off.
U.S. Patent Application Number 2004/0137288 (filed Oct. 16, 2003; Morgenstern) teaches a process for reforming an alcohol that comprises of contacting an alcohol with a reforming catalyst comprising copper at the surface of the metal supporting structure or sponge in the form of a powder (20 to 65 microns in size) or pellet, which is preferably a metal sponge supporting structure comprising nickel. A catalyst in the form of a monolith produced by incorporating the catalyst onto the surface of a suitable substrate (e.g. honeycomb) is also taught. While the application describes the composition of a catalyst and a method for conducting the reformation of alcohol at temperatures below 400° C., it does not teach a reactor and method for loading the fine catalyst particles (20 to 65 microns in size) in a practical manner that can be used in the process train of an internal combustion engine. While feeding a 70 wt.-% ethanol/water mixture to a reactor containing 2 grams of copper coated (on nickel) catalyst powders at 280° C., and at a flow rate of 0.3 ml/min with 100 sccm of nitrogen diluent, the pressure inside the reactor increased from 28 psig to 80 psig. The reactor consisted of a stainless steel tubular reactor that was wrapped with a coiled heater.
What is needed is a compact reactor that can use the low sensible heat of the exhaust gases to convert a fuel or a portion thereof to a gas mixture consisting of methane, carbon oxide and hydrogen. Preferably, the fuel should be lean in steam so as to reduce the endothermicity (heat requirement) of the reforming reaction. As is known to those skilled in the art, carbon deposition (coke formation) is a problem when fuels that are lean in steam are reformed. The reactor and catalysts and the method adopted for reforming should therefore mitigate or prevent coke formation. Since the exhaust gases exit the engine at low pressure, the reforming reactor and associated components (catalysts, fittings, etc.) should not introduce pressure into the internal combustion engine while operating over a wide range of fuel feed rates. Furthermore, the reactor and reactor components should be low in cost. Finally, the reactor should be capable of acceptable catalysts in the forms of powders, pellets, coated porous supports such as metal or ceramic foams or monoliths or coatings on the surfaces of the reactor.
The use of catalysts in the pellet form is a reliable, low-cost, but less efficient approach. These catalysts are suitable for use in processes where reactor size is not a critical parameter (e.g. refineries, process plants). Reactors containing catalyst pellets are not suitable for on-board reforming for the ICE application.
The use of catalyst powders (<100 microns in size) can be considered to be an approach that yields a compromise between the high efficiency of wash-coated catalysts and the low-cost of the pelletized catalysts. However, loading fine powder material directly into the reaction chambers results in an undesirable pressure drop when the packed reaction chambers are exposed to fluid flow. This is due to agglomeration of the fine particles. The ICE train is a low pressure train, and therefore a reformer that leads to high pressure drop (>5 psig) or high inlet pressures (>5 psig) would not be a good fit for ICE use.
Morgenstern and Fornango (Energy Fuels, 19 (4), 1708-1716, 2005) describe the use of copper coated Raney nickel powder as a catalyst for reforming a fuel consisting of 70 vol.-% ethanol in water. While feeding fuel at a rate of 0.1 ml/minute at 265° C. over 2 grams of the catalyst packed in a reactor tube, a gas mixture rich in methane, carbon monoxide and hydrogen was produced for 400 hours in a somewhat stable fashion. The reactor pressure was 4 psig even at this low flow rate.